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Sweet corn

Chris Carson carson at teosinte.agron.missouri.edu
Mon Nov 22 15:01:13 EST 1999

These are important genes for the sweetcorn world!
For lots of information,please try using the Maize Genome Database:
here's how:

sh2 - shrunken2 - gene involved in "supersweet" sweetcorn, but named for

its dry kernel appearance.
First, because we know the names of the genes that we are interested in,

search in the locuslite form:
for sh2:
As you scroll and read, notice that the gene is cloned, it is located in
an information-rich region of the genome (heavily mapped), and there is
a large allele series (great genetic diversity).  Notice the
descriptions, the gene sequence information and the abundant reference
list, including the Genelist citation in the reference contents that
identifies who first described sh2 as a gene:  Mains, EB. 1949
Although, its "sweet" phenotype can be accredited to Dr. John R.

See also images of sh2 mutant kernels from the Variations with Images
link on the LocusLite sh2 page that leads to:

su1 - sugary1 - classic sweetcorn gene, named for its sweet phenotype
search in the locuslite form for su1
Notice that the su1 gene has also been cloned.
First described by Correns, C. 1901
This mutation in the homozygous condition (su1/su1 sweetcorn) was
utilized by the Native people of America.  In this regard, we can be
relatively sure that those people didn't use modern genetics or
mutagens, but they can certainly be credited with some plant breeding
productivity (selecting quality germplasm of the variation for the best
production next season).  Variations with Images links to images of su1
(compare to sh2 image):

se1 - sugary enhancer1 - modifies su1 phenotype
It is not sweet itself when homozygous, but effective when homozygous
with homozygous su1.
Using the locuslite form for se1:
The Genelist link in the reference list indicates the first genetic
description of se1 (Ferguson, JE et al. 1978):

The bottom line is that two of these mutants are essential for most
sweet corn production (sh2 and su1, but there are others. such as the
triple mutant combination: ae1/ae1, du1/du1, wx1/wx1).  In each case,
the major contribution to the sweetness of sweet corn is due to these
genes, however the quantity of the sweetness, and the quality of the
flavor and texture can be influenced by yet other genes (se1 for
example) and it is the combinations of these genes (alleles) that a
plant breeder is interested in manipulating.  Remember too that the goal
is to disrupt starch production so to accumulate sugar, but not disrupt
endosperm (seed) development too badly (see the dry seed mutant
phenotypes of each in the images mentioned above, sh2 mutants can be
quite lethal and difficult to germinate). Personally, I have tasted
several different cultivars of sh2 sweetcorn side-by-side and the flavor
qualities between them were surprisingly different.  They were all
sh2/sh2, but the background combination of other gene alleles really
varied the flavor.  The same would be true for su1/su1 corn, such as in
the case of the se1 gene.

Chris Carson
Missouri Maize Project
Agronomy - Curtis Hall
University of Missouri
Columbia, MO 65211
carson at teosinte.agron.missouri.edu
voice mail: 573-882-0832

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